Demons

They are summoned by the group of the Summoners.

Appearance and power
Demons can be very different depending on the amount of power they have. The smaller ones are the weakest, but the strong ones can also control their size thanks to their powers. The weakest Summoners summon the weakest demons. Also, the stronger demons can fly. The weakest usually are beasts that creep on the ground.

The power to summon stronger beasts increases when the demons kill people, having their souls as a source of power. To be able to summon strong demons, the demon must first get that source of power.

Origins
At first the Summoners thought they could use them to help people and to make things easier for the humans, because they obeyed everything the Summoners told them to do. But later, the Summoners started to think that if they were the only ones with the gift of summoning, they should use the demons only for the Summoners benefits. It was then when their purposes started to be full of dark thoughts, and it ended with demons killing persons, in order to make their Summoner stronger.